Percentage Error Calculator

Reviewed by CalcMulti Editorial Team·Last updated: March 2026·← Percentage & Ratio Hub

Percentage error compares an experimental (measured) value to a known theoretical (accepted) value. Formula: % Error = |Experimental − Theoretical| / |Theoretical| × 100. The absolute value signs mean the result is always non-negative — a 5% error whether your measurement is high or low.

Percentage error is fundamental in physics, chemistry, and engineering labs. It quantifies how accurate your measurement was. A 1% error is excellent; 5% is acceptable in many contexts; above 10% usually indicates a systematic problem with method or equipment.

For example, if you measure the density of water as 0.98 g/mL when the accepted value is 1.00 g/mL: % Error = |0.98 − 1.00| / |1.00| × 100 = 0.02 / 1.00 × 100 = 2%.